Oroville Dam failure has Santa Cruz officials allaying fears

Loch Lomond Reservoir and its Newell Creek Dam were constructed in 1960. City of Santa Cruz officials do not fear the same type of damage for its drinking water storage as seen at Oroville Dam. (City of Santa Cruz Water Department — Contributed)

Newell Creek Dam’s concrete siding has been built to a height for withstand a force five times that seen in the area’s devastating 1982 flood. (City of Santa Cruz Water Department — Contributed)

DISASTROUS HISTORY

Historically, there have been no reported failures of the Newell Creek Dam, even after 1989’s Loma Prieta earthquake. The only significant known danger the dam has posed to the local community came in late 1960, near completion of the $1.6 million structure. On Oct. 25, four construction workers were killed, buried beneath an earth slide when a 100-foot cliff collapsed at the dam while workers drilled a hole for grouting, according to Sentinel archives.

A plaque commemorating Floyd Gordon, 43, of Redding, Alton Thomas, 31, of Watsonville, Everitt McIntosh, 60, of Santa Cruz and Gerald Kenly, 30, of Santa Cruz, was installed at the dam’s commemoration ceremony in August 1961.

BEN LOMOND >> Some 10 miles north of the city of Santa Cruz, Loch Lomond Reservoir’s maximum 2.8 billion gallons of water is held in check by the 56-year-old Newell Creek Dam.

When news broke of the evacuation of more than 200,000 residents north of Sacramento near Oroville Dam last week due to spillway damages, Santa Cruz Deputy Water Director Heidi Luckenbach said she thought area residents might automatically begin to worry about the safety of their own dam.

“I don’t know how many people really realize that they have a dam upstream of them,” Luckenbach said. “To the extent that this makes people think about that, because they’re seeing it in the news, it would be great to be able to share that we have a dam, but that we have all these other things in place that do ensure its safety.”

As with its much larger cousin Oroville Dam, the city of Santa Cruz’s reserve drinking water supply is contained within an earthen dam that offers flood protection through a concrete-lined spillway. The spillway is about 13 feet below the top of the dam, as a measure of controlled release for flood prevention.

Both Oroville Dam’s main and emergency spillways were damaged by high water flows during recent storm runoff buildup.

Santa Cruz resident Stanley Sokolow was among those who questioned local safety conditions in this season of high rainfall. The city of Santa Cruz is on course to double its average annual rainfall this season, and the Loch Lomond Reservoir watershed has received roughly double the city’s precipitation.

“Here in Santa Cruz County, we have had extensive damage to hillside roads due to the unusual amount of rainfall,” Sokolow wrote in an email to the Sentinel. “Could Loch Lomond dam be next?”

Newell Creek Dam uses two secondary outlet drains coming out the “toe” of the dam, unlike Oroville Dam’s unlined emergency spillway. The slope around Oroville’s emergency spillway, which had not been used previously in the dam’s 50-year lifetime, began eroding when called into action last week.

Spillover Plan

Were Newell Creek Dam’s main spillway to suffer damage, as with Oroville’s, Santa Cruz would use its Newell Creek Pipeline, leading to the Graham Hill Water Treatment Plant along Pipeline Road, and/or a larger 36-inch emergency release pipeline to reduce the reservoir’s water level as needed, Luckenbach said. Water flow to the pipelines is controlled through a series of five gates, all of which were replaced within the past five years, she said. In January and February, the Newell Creek Pipeline experienced three leaks, the first of which forcing the city to draw from emergency backup drinking water supplies for four days and a request for customers to cull their usage. The emergency pipeline, which only has been used for routine testing thus far, has a capacity from five to seven times Newell Creek Pipeline’s, Luchenback said.

“We spill, like, seven in 10 years and we don’t spill in the summertime. So we have a lot of opportunity to go out and do inspections, both of the spillway and the surrounding. I think with Oroville, on the one side, there was noticeable subsidence,” Luckenbach said. “We have areas on both side we can do inspections on those as well, to make sure nothing is happening.”

The city is in the midst of updating its emergency action plan, work Luckenbach expects to concluded before the end of the year. For now, the department looks to a plan first developed by Santa Cruz County in the 1980s, she said. Recently, the county completed its updated Local Hazard Mitigation Plan 2015-2020, with a chapter devoted to dam failure.

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“The losses to life and property associated with complete dam failure would be high,” the county hazard plan states. “Given the monitoring protocol at the Newell Creek, the probability of dam failure is very low.”

The regulatory state Division of Safety of Dams conducts annual inspections at Loch Lomond. Additionally, the city conducts regular local monitoring of the dam, the area surrounding the reservoir, the spillway and drains known as weirs that collect any naturally escaping water that seeps through the dam, Luckenbach said.

In 2009, the city conducted testing to ensure the dam is up to the latest seismic safety standards, she said. In the mid-1980s, the dam’s main spillway walls were raised to a height about five times the force of the devastating 1982 flood, according to Sentinel reports.

Loch Lomond Reservoir holds a quarter of a percent of Lake Oroville’s capacity and stands 182 feet high to Oroville’s 770 feet, according to Army Corps of Engineers’ National Inventory of Dams database. Of California’s 1,585 dams, nearly 75 percent are earthen in construction. More than a third of the state’s dams were built from 1950 to 1970, federal statistics show.

DISASTROUS HISTORY

Historically, there have been no reported failures of the Newell Creek Dam, even after 1989’s Loma Prieta earthquake. The only significant known danger the dam has posed to the local community came in late 1960, near completion of the $1.6 million structure. On Oct. 25 of that year, four construction workers were killed, buried beneath an earth slide when a 100-foot cliff collapsed at the dam while workers drilled a hole for grouting, according to Sentinel archives.

A plaque commemorating Floyd Gordon, 43, of Redding, Alton Thomas, 31, of Watsonville, Everitt McIntosh, 60, of Santa Cruz and Gerald Kenly, 30, of Santa Cruz, was installed at the dam’s commemoration ceremony in August 1961.

About the Author

Jessica A. York covers Santa Cruz city hall, Santa Cruz City Schools, Soquel Creek Water District and homeless issues for the Sentinel. She has been a working journalist, on both coasts, since 2004. Reach the author at jyork@santacruzsentinel.com
or follow Jessica A. on Twitter: @reporterjess.